1. Field of the Invention
The present invention relates to an on-chip transformer balun, and more particularly, to an on-chip transformer balun capable of sustaining a larger current than a conventional transformer.
2. Description of the Prior Art
Regarding current on-chip transformer baluns, the method of winding in different layers may cause an obvious parasitic-effect problem and decrease the coupling coefficient. However, there is another winding method of winding in the same layer for increasing the coupling coefficient but the winding ratio may not be increased owing to the limited layout area. Moreover, due to the properties of manufacturing process of semiconductor, the circuit on the uppermost layer can sustain a higher current density than the circuit on other layers. Therefore, if the winding has breaches required to be connected by metal bridges, the sustainable current density of the whole circuit would be confined to the sustainable current density of circuits on other layers. As a result, the request of high-to-low impedance transformation is not achieved; especially in the field of power transformation, being unable to increase the ratio of impedance transformation indicates that more transformation stages are required. Namely, the more layout area is required, the more power is lost in the transformation.
Accordingly, providing a transformer balun capable of sustaining a larger current than a conventional transformer is requested.